The invention relates to a cuvette for optical gas-analysis apparatus, particularly infra-red gas-analysis apparatus, and consisting of a metallic housing with two end-faces and a longitudinal axis and two chambers, which are parallel to the longitudinal axis and have radiation-reflecting wall surfaces and are separated from each other by a partition, one of which chambers is provided for accommodating the gas under investigation and the other for accommodating a reference gas, the chambers being closed off at the end-faces by radiation-penetrable windows made of a material from the group, calcium fluoride and barium fluoride, and which are initially connected by way of a glass solder to an intermediate frame, which is in turn connected to the housing.
DE-OS No. 27 20 636 discloses a cuvette of this kind which is arranged within a pneumatic infra-red radiation detector. This publication does not however describe in detail, the connection between the jar housing and the radiation-penetrable windows. It is simply stated that the radiation-penetrable window of the detector, which contains a micro-current sensor, is connected in a vacuum-tight manner to a thin-walled cup, made of noble metal, by means of a special glass solder.
In the manufacture of a known cuvette used in practice, the procedure has been to connect the radiation-penetrable windows to a silver intermediate frame initially by means of a glass solder. The windows prepared in this way have then been connected to the housing of the cuvette by means of a soft solder and a flux. The solder had a melting point of approximately 200.degree. C. When soldering with a flux, there is the danger that the flux will penetrate into the zone of the radiation-reflecting wall surfaces of the cuvette and will etch them, so that the cuvettes are rendered unusable. The required radiation-reflection on the part of the wall surfaces is generally achieved by means of a very bright coating of gold. Such glass solder-metal solder connections cannot of course be used for temperatures above approximately 150.degree. C.
It is also known to connect the radiation-penetrable windows to the housing of a cuvette by means of a synthetic resin adhesive. Although such adhesives can be used at temperatures up to approximately 250.degree. C. and slightly more, none of these adhesives is sufficiently resistant to penetration by water-vapor. Penetration of water-vapor into the reference cell must, however, be prevented at all costs. Hitherto, special absorption means have been provided for this purpose, but their effect diminishes with rising temperatures because of increasing desorption.